This group has continued its analysis of sequence-specific DNA- binding proteins in Drosophila, with focus on the heat shock genes and the segmentation gene fushi tarazu. For the heat shock genes, the critical regulatory transcription factor, heat shock activator protein (renamed heat shock factor, HSF) has been purified to homogeneity repeatedly; anti-HSF antibodies have been produced, and candidate gene clones of HSF have been identified in a lambda gtll expression library. In addition, purification and characterization of the other transcription factor found to bind to the heat shock promoter (at the TATA box) is under way. A screen for DNA-binding proteins that interact with the "zebra" control element of the fushi tarazu gene that is expressed in alternate segmental primordia early in Drosophila embryogenesis around the blastoderm stage has been completed using nuclear extracts of developmentally staged embryos. At least 3 major pro- teins or protein complexes were observed to bind specifically to a region encompassing 200 bp upstream of the transcriptional start site. One factor, NF-ftzl has been purified to homogeneity, antibodies have been generated, and the cloning of its gene is in progress. The biochemical purification and subsequent cloning of the factors that interact with these genes should provide the important reagents necessary for the next stage of analysis of mechanisms of regulation of cellular homeostasis and of segmental determination.